Mechanical hammer and like impact tool



Aug. 31, 1937. F. M. LEWIS 2,091,408

MECHANICAL HAMMER AND LIKE IMPACT TOOL Filed Oct. 29, 1936 Patented Aug.31, 1937 MECHANICAL HAMMER AND LIKE IMPACT TOOL Frank Michael Lewis,London, England Application October 29, 1936, Serial No. 108,301

In Great Britain November 1, 1935 2 Claims.

This invention relates to mechanical hammers, rock drills, caulking andriveting tools and like percussive tools or impact devices of thekindcomprising in a single cylinder a mechanically op- 5 erated main orworking piston and a second piston linked to the first'mentioned pistonpneumatically to be actuated thereby and constituting the operativepiston of the tool.

Impact devices of this character have before been proposed having one ormore ports in the cylinder controlled by the operative piston in such away as to be automatically closed when the tool carried by the operativepiston is in contact with the work and to be opened when the pressure ofthe work on the tool is removed.

The object of the present invention is to devise improvements in theconstruction and arrangement of impact devices of the kind referred towhich will render them more certain and powerful in operation, and theinvention consists in an impact device of the kind referred to having aport in the cylinder controlled by the main piston and also by anon-return valve through which inhalation of air into the space betweenthe pistons may take place so as to ensure that there shall always be anair cushion between the pistons.

Further features of the invention will be apparent from the descriptiongiven hereafter.

The accompanying drawing illustrates one mode of carrying out theinvention.

Figure 1 is a longitudinal sectional elevation of one convenient form ofmechanical hammer in accordance with the invention and Figure 2 is aside view of Figure 1 partly in section and partly in elevation.

In carrying my invention into effect in one convenient manner I form myimproved apparatus with a cylinder at of suitable size and shape inwhich is a main or working piston b operated from a prime mover byflexible shafting or otherwise or operated by a portable prime moverforming part of the tool itself, it being thought unnecessary toindicate any particular means of operation in the drawing since anysuitable source of power and any convenient form of connection may beemployed.

The cylinder 0. also contains a floating piston c which may be termedthe operative piston, and which is adapted to co-operate with an anvil d50 holding the chisel e or other tool and which is allowed a limitedamount of movement, the anvil, for example, being formed with a shoulderal working in a recess at the base of the main cylinder.

55 Furthermore, the chisel or other tool may be provided with a collaror the like g adapted to co-operate with a stop it so that the chisel orother tool' is prevented from falling away from the device.

The cylinder a. is provided with two sets of 5 ports 2' k respectively,such ports being spaced apart as shewn and such that when the operativepiston c is in its free or neutral position the ports is which may betermed the neutral ports, are just above the upper end of the piston c.In 10 addition the main cylinder is provided with a port 1 controlled bythe working piston b and also by a non-return valve m permitting of theingress of air into the cylinder while preventing its egress therefrom.The clearance between the 5 working piston b when at the bottom of itsstroke and the operative piston 0 when in its working position as shewnin Figure 1 (that is when pushed upwards by the anvil when the tool ispressed into contact with the work) is relatively small. 20

The whole arrangement may be in an outer casing n designed to protectthe ports and valve from the entry of dirt or foreign matter, the casingbeing provided with one or more small openings 0 to permit of the entryof air into the 25 annular space between the casing and cylinder.

The operation of the device is as f01l0Ws:-

Normally with the piston c in its lowermost position the ports 70 willbe open and in consequence when power is applied to the device to movethe working piston 19 such movement will not cause any movement of theoperative piston and the tool will thus be in neutral. So soon, however,as the tool is pressed into contact with the work the anvil moves intothe position shewn in Figure 1, so that the neutral ports are closed bythe operative piston and thereupon upward movement of the workingcylinder b causes the operative piston also to move upwards, therebeing, however, a lag between the two movements so that when the workingpiston is at the top of its stroke, the non-return valve m is open andslight inhalation of air takes place due to the reduction in pressure inthe space between the two pistons. When the working piston starts todescend it meets the operative piston still ascending and thesemovements continue until the clearance between the pistons becomes smallwhen the pressure between the pistons rises to an amount sufficient togive the operative piston a downward movement which is designed to takeplace when the working piston b is moving at its greatest speed, thatis, when the crank is at right angles. The operative piston now travelsmore quickly than the working piston and delivers its blow upon theanvil.

The purpose of the non-return valve m is to ensure that there shallalways be an air cushion between the two pistons so that if any airleakage takes place the pistons will not come into contact with oneanother.

An arrangement such as above described operates quite satisfactorily solong as the piston 1) allows a certain amount of leakage to take placefrom the space between the pistons, but it is found in practice that ifthe piston does not permit of such leakage, the pressure between thepistons will eventually rise to such an extent that the hammer willcease to function. In such cases, therefore, it is necessary to providea further valve m which may be similar to the valve m except that itopens under pressure instead of under suction and when the'operativepiston is in its lowest position. Thus at the bottom of the stroke thevalve m opens and allows the air between the pistons to reach aboutatmospheric pressure. At the top of the stroke the valve m opens andallows air to be admitted to make up leakage and to allow the blow to bedelivered without any (or much) negative force to be given to theoperative piston, the ideal being that the blow is delivered when thecrank is at right angles and that the pressure between the pistonsshould be at about atmospheric pressure when the blow is delivered. 0nthe further movement of the main or working piston, the pressure isrelieved by the opening of the valve 122 I claim:

1. An impact device of the kind referred to comprising a cylinder, apower-driven piston in said cylinder, a second piston linkedpneumatically to the first mentioned piston and constituting theoperative piston of the tool, said cylinder having two sets of ports,one situated at the lower end and another set situated just above theoperative piston when the latter is in its inoperative position andconstituting the neutral ports of the tool, said cylinder further havinga port controlled by the working piston and also by a non-return valvethrough which inhalation of air into the space between the pistons maytake place, and a non-return valve controlling a further port in saidcylinder to relieve the pressure between the pistons when the operativepiston is at the bottom of its stroke.

2. An impact device comprising the combination of claim 1 and havingalso an outer casing enclosing the main cylinder and non-return valvesand furnished with one or more small openings to permit of the entry ofair into the annular space between the casing and cylinder.

